# std::ctype

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< cpp‎ | locale

Defined in header `<locale>` |  |
template< class CharT > class ctype; |  |

Class `ctype` encapsulates character classification features. All stream input operations performed through std::basic_istream<CharT> use the `std::ctype<CharT>` of the locale imbued in the stream to identify whitespace characters for input tokenization. Stream output operations apply `std::ctype<CharT>::widen()` to narrow-character arguments prior to output.

Inheritance diagram

### Specializations

The standard library is guaranteed to provide the following specializations (they are required to be implemented by any locale object):

Defined in header `<locale>`
`std::ctype<char>` | provides narrow character equivalents of the minimal "C" locale classification. This specialization uses table lookup for character classification
std::ctype<wchar_t> | provides wide character classification appropriate to the native character set

### Nested types

Type | Definition
`char_type` | `CharT`

### Data members

Member | Description
std::locale::id `id` [static] | the identifier of the facet

### Member functions

(constructor) | constructs a new `ctype` facet (public member function)
(destructor) | destructs a `ctype` facet (protected member function)
is | invokes `do_is` (public member function)
scan_is | invokes `do_scan_is` (public member function)
scan_not | invokes `do_scan_not` (public member function)
toupper | invokes `do_toupper` (public member function)
tolower | invokes `do_tolower` (public member function)
widen | invokes `do_widen` (public member function)
narrow | invokes `do_narrow` (public member function)

### Protected member functions

do_is [virtual] | classifies a character or a character sequence (virtual protected member function)
do_scan_is [virtual] | locates the first character in a sequence that conforms to given classification (virtual protected member function)
do_scan_not [virtual] | locates the first character in a sequence that fails given classification (virtual protected member function)
do_toupper [virtual] | converts a character or characters to uppercase (virtual protected member function)
do_tolower [virtual] | converts a character or characters to lowercase (virtual protected member function)
do_widen [virtual] | converts a character or characters from char to `CharT` (virtual protected member function)
do_narrow [virtual] | converts a character or characters from `CharT` to char (virtual protected member function)

## Inherited from std::ctype_base

### Nested types

Type | Definition
`mask` | unspecified BitmaskType type (enumeration, integer type, or bitset)

### Member constants

space [static] | the value of `mask` identifying whitespace character classification (public static member constant)
print [static] | the value of `mask` identifying printable character classification (public static member constant)
cntrl [static] | the value of `mask` identifying control character classification (public static member constant)
upper [static] | the value of `mask` identifying uppercase character classification (public static member constant)
lower [static] | the value of `mask` identifying lowercase character classification (public static member constant)
alpha [static] | the value of `mask` identifying alphabetic character classification (public static member constant)
digit [static] | the value of `mask` identifying digit character classification (public static member constant)
punct [static] | the value of `mask` identifying punctuation character classification (public static member constant)
xdigit [static] | the value of `mask` identifying hexadecimal digit character classification (public static member constant)
blank [static] (C++11) | the value of `mask` identifying blank character classification (public static member constant)
alnum [static] | alpha | digit (public static member constant)
graph [static] | alnum | punct (public static member constant)

### Example

The following example demonstrates modification of a `ctype` other than `ctype<char>` to tokenize a CSV file:

Run this code

    #include <iostream>
    #include <locale>
    #include <sstream>

    struct csv_whitespace : std::ctype<wchar_t>
    {
        bool do_is(mask m, char_type c) const
        {
            if ((m & space) && c == L' ')
                return false; // space will NOT be classified as whitespace

            if ((m & space) && c == L',')
                return true; // comma will be classified as whitespace

            return ctype::do_is(m, c); // leave the rest to the base class
        }
    };

    int main()
    {
        std::wstring in = L"Column 1,Column 2,Column 3\n123,456,789";
        std::wstring token;

        std::wcout << "default locale:\n";
        std::wistringstream s1(in);
        while (s1 >> token)
            std::wcout << "  " << token << '\n';

        std::wcout << "locale with modified ctype:\n";
        std::wistringstream s2(in);
        csv_whitespace* my_ws = new csv_whitespace;
        s2.imbue(std::locale(s2.getloc(), my_ws));
        while (s2 >> token)
            std::wcout << "  " << token << '\n';
    }

Output:

    default locale:
      Column
      1,Column
      2,Column
      3
      123,456,789
    locale with modified ctype:
      Column 1
      Column 2
      Column 3
      123
      456
      789

### See also

ctype<char> | specialization of std::ctype for type char (class template specialization)
ctype_base | defines character classification categories (class)
ctype_byname | represents the system-supplied std::ctype for the named locale (class template)

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